Take a home test on your first void of the day, if you pass that then you'll be good for your test (which you should still drink a powerade and void a few times before). IF you fail the home test, then look into diluting or substitution, but no point in doing all of that if you're already clean. If you get caught subbing your in a lot of trouble, if they detect you diluted you will have to retest (which isn't the worst thing). But the moral is, if your clean, why risk it? Take a home test, then go on to the next steps.